Compounds of formula I:
and pharmaceutically acceptable salts thereof, useful as protein kinase C inhibitors, were disclosed by Heath, et al., in European Patent Publication No. 817,627 (Heath).
Example #49 of Heath disclosed a free base compound of formula FB:

While FB is undoubtedly a very effective pharmaceutical agent, unexpected difficulties were encountered in its large-scale production. Thus, unpredictable formation of solvates complicated the commercial synthesis to such an extent that it became necessary to develop an alternative form for large-scale commercialization.
In this context, WO 02/02094 and WO 02/02116 specifically describe the use of the dihydrochloride salt of FB (FB-2HCl) to treat cancer and to inhibit tumor growth as a mono-therapy or in conjunction with an anti-neoplastic agent or radiation therapy. Unfortunately, it has now been determined that FB-2HCl is hygroscopic. In addition, although FB-2HCl appears to be crystalline by optical light microscopy, more detailed study by X-ray powder diffraction (XRD) has revealed that this material is in fact only poorly crystalline.
Surprisingly, in accordance with the invention, it has now been discovered that the monohydrochloride salt of FB is capable of being reproducibly produced on a commercial scale, is not significantly hygroscopic, is sufficiently stable for use in oral formulations, and can be produced in a highly crystalline state.